Foams, such as polyurethanes (PUs), are abundant and play an important role as thermal and sound insulators in many industries, for example, shipbuilding, footwear, construction, cars, electronics and sporting goods. PUs are often prepared by the reaction of di-isocyanates or poly-isocyanates with polyols. PU foams may be produced, for example, by the reaction between isocyanate and water to produce a substituted urea and gaseous carbon dioxide. The carbon dioxide may function as the blowing agent in the production of the PU foam. See Klempner, D., Sendijarevi, V. et al. (2004) Handbook of polymeric foams and foam technology, Munich, Germany.
PUs can also be synthesized from components derived from vegetable oils such as soybean, palm, castor, sunflower, canola and linseed. Soybean oil is a common plant-based material used for the synthesis of polyols which are ultimately used for the production of PUs. For example, soybean oil has been used in such a manner in diverse application areas such as coating, paint formulation and foams. See Guo, A., I. Javni, et al. (2000) “Rigid polyurethane foams based on soybean oil” Journal of Applied Polymer Science 77(2): 467-473; Petrovic, Z. S. (2008) “Polyurethanes from vegetable oils” Polymer Reviews 48(1): 109-155.
The source of di-isocyanates or poly-isocyanates, however, used to prepare PU foams is predominately petroleum-based. Isocyanates are considered by the US Environmental Protection Agency (EPA) to be toxic. The EPA recently announced that di-isocyanates face EPA regulation due to adverse health effects such as breathing and skin problems and are considered by the Occupational Safety and Health Administration (OSHA) to be the leading cause of work-related asthma. See EPA (2011) “Methylene Diphenyl Di-isocyanate (MDI) and Related Compounds Action Plan”; EPA (2011) “Toluene Di-isocyanate (TDI) Action Plan”. The EPA intends to target TDI and MDI by issuing a rule under the Toxic Substances Control Act (TOSCA) to require industry to notify the EPA before using TDI and MDI and their related products such as dimers, trimers and polymers. Therefore, current PU foams have considerable toxicity, regardless of being labeled “bio-based” or petroleum based. For instance, commercially available “bio-foam” may be prepared using a soyoil based polyol, but the di-isocyanate compounds (i.e., petroleum-based) are still required. This “bio-based foam”, which is the current state of the art, is typically less than about 30% bio-based and still retains considerable toxicity due to the use of di-isocyanates.
Accordingly, there is a need for foams with desired chemical and physical properties, such as density and robustness, that are also predominantly bio-based and have limited or no toxicity. The foam described in the present disclosure has suitable physical and chemical properties to be applicable in a wide range of applications while also being substantially free of petroleum-based products. One of the benefits of the composition of the present disclosure is the removal of, or substantial removal of, isocyanates (e.g., di-isocyanates) from the foam. The foam described in the present disclosure is substantially, and in some embodiments completely, free of di-isocyanates, poly-isocyanates, and/or similar groups.
Similar foams made using only a single component have been reported. See Bonnaillie, L. M. and R. P. Wool (2007) “Thermosetting foam with a high bio-based content from acrylated epoxidized soybean oil and carbon dioxide” Journal of Applied Polymer Science 105(3): 1042-1052. These foams contain only acrylated epoxidized soyoil (AESO) and are characterized by densities of greater than or equal to 15 lb/ft3. Light and very light foams of lesser density were not achieved by Bonnaillie, et al.
Furthermore, foams containing AESO alone tend to form defects, such as cracks, due to the incomplete reaction of the functional groups. It is well known that AESO when polymerized by itself forms elastomeric materials that tend to have a fragile consistency due to many defects existing in the resulting cross-linked structure. Bonnaillie et al. reported AESO foam having only about 64% of the acrylate groups having undergone reaction. As such, the Bonnaillie et al. foams also do not have sufficient mechanical integrity. For example, cracks were found in the Bonnaillie et al. foams which reduce the strength of the foams. For thermal insulation and many engineering and packaging applications, densities of about 1 to about 8 lb/ft3 are preferred in addition to significant mechanical properties and durability. Thus, the foams described by Bonnaillie et al. are not suited to the broad range of engineering applications currently addressed by such petroleum-based foams as polyurethanes.